Philo of Alexandria lists several examples of things that human beings will never know, one of which is whether the moon shines of its own light or merely reflects the light of the sun. Subsequent history has proven conclusively that he was mistaken. The lesson that I draw from this is that both a certainty of knowledge and a certainty of ignorance are equally precarious. We have seen how the meaning of “God is one” is fundamentally implicated with the question of knowledge of God, but I will not here hazard a conclusion regarding whether knowledge of God is easy, difficult, possible, impossible, or impious as our various Jewish thinkers have argued. And yet our history ought to be able to provide some conclusion about what “God is one” means in a Jewish context.